1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a transflective liquid crystal display device using an optically compensated bend (OCB) alignment technique which can realize an increase in viewing angle and an increase in response speed.
2. Description of the Related Art
Liquid crystal display devices have been applied to various fields by taking advantage of their features such as light weight, small thickness and low power consumption.
In recent years, attention has been paid to a liquid crystal display, to which the OCB mode is applied, as a liquid crystal display device which can improve the viewing angle and response speed. The OCB mode liquid crystal display device is configured such that a liquid crystal layer including liquid crystal molecules, which are bend-aligned in a state in which a predetermined voltage is applied, is held between a pair of substrates. Compared to a twisted nematic (TN) mode, the OCB mode is advantageous in that the response speed can be increased and the viewing angle can be increased since the effect of birefringence of light, which passes through the liquid crystal layer, can optically be compensated by the alignment state of liquid crystal molecules.
In addition, in recent years, a transflective liquid crystal display device having a reflective part and a transmissive part has been developed. Jpn. Pat. Appln. KOKAI Publication No. 2005-164957, for instance, discloses a circular polarizer which is applicable to an OCB mode transflective liquid crystal display device. This circular polarizer is configured to include a polarizer and a liquid crystal film as an optical anisotropic element in which a nematic hybrid alignment structure is fixed.
At present, however, in the transparent liquid crystal display device to which the OCB mode is applied, for example, with respect to a blue pixel of 430 nm, black voltages do not agree in reflective display and transmissive display, and a black voltage in transmissive display is higher than a black voltage in reflective display. At this time, if the black voltage in transmissive display is commonly applied, as an optimal black voltage, to the transmissive part and reflective part of the pixel, the reflectance in the reflective part does not become zero, and owing to this effect, gray level inversion is visually recognized when the liquid crystal display device is observed in a frontal direction.
Similarly, with respect to the long wavelength side, for example, with respect to a red pixel of 625 nm, black voltages do not agree in reflective display and transmissive display, and a black voltage in transmissive display is lower than a black voltage in reflective display. At this time, if the black voltage in transmissive display is commonly applied, as an optimal black voltage, to the transmissive part and reflective part of the pixel, the reflectance in the reflective part does not become zero, and a gray level value corresponding to black cannot be obtained. Thus, perfect black display cannot be effected when the liquid crystal display device is observed in a frontal direction.